1. Field of the Invention
The present invention relates generally to a video signal processing circuit, and is directed more particularly to a video signal processing circuit for use in a television receiver.
2. Description of the Prior Art
In the prior art, a video signal applied to drive the cathode of a cathode ray tube is selected such that, as shown in FIG. 1, the screen of the cathode ray tube becomes darkest at a pedestal level V1 of the video signal and becomes brightest at a white level V2 of the video signal. This is accomplished by setting the cut off level of the cathode ray tube (at which the screen becomes black) at the pedestal level of the video signal, thus completely restoring the D.C. component. In this situation, any change from station to station of the set up level of the video signal (i.e., the small difference between the pedestal level and the black signal level) is manifested as a change in the black signal level, with the result that when a broadcast signal of a station with a large set up level is received, the black parts of the picture appear somewhat gray. To avoid this defect, in a prior art television receiver the D.C. transferring ratio is lowered to a value in the range of about 0.5 to 0.9, causing fluctuations in the black level due to fluctuations in the set up level to be relatively small. However, the fluctuation of the black level can not be sufficiently removed in this manner.